Twitter is modifying its search engine to include tweets more than a week old, a move it said will help users uncover better content.

Over the next few days, searches will return "a fairly small percentage of total tweets ever sent" but that will increase over time, wrote Paul Burstein, an engineer who works on Twitter's search infrastructure, on a company blog.

"We look at a variety of types of engagement, like favorites, retweets and clicks, to determine which tweets to show," Burstein wrote. "We'll be steadily increasing this percentage over time, and ultimately, aim to surface the best content for your query."

The change comes a day after Twitter updated the search function in its iOS and Android mobile applications to return a blend of tweets, photos and people in a single stream of results, rather than having separate tabs for tweets and people.

Twitter also made other changes to streamline the mobile apps. Content from the "Discover" tab, which has items such as tweets, activity notices, trending topics and suggestions of new people to follow, are now also in a single stream.

How users interact with links to websites has also been changed, allowing people to go directly to a linked website without having to open the tweet, saving a bit of time.